To meet the demand for wireless data traffic, which has increased since the deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’.
It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like.
In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple Access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed.
In broadband carrier transmission which recently emerges as a 5G communication and uses a mmWave band, each transmission (Tx) antenna is used as an array antenna, so a beam gain may be acquired through radio frequency (RF) beamforming. In this case, a user equipment (UE) performs a beam sweeping process for each Tx antenna, and selects an optimal Tx antenna and an optimal Tx beam based on a result of the beam sweeping process.
An environment where there is a mismatch between uplink coverage and downlink coverage in a general mmWave communication system will be described with reference to FIG. 1.
FIG. 1 schematically illustrates an environment where there is a mismatch between uplink coverage and downlink coverage in a general mmWave communication system according to the related art.
Referring to FIG. 1, it will be assumed that the mmWave communication system is an institute of electrical and electronics engineers (IEEE) 802.11ad communication system.
Referring to FIG. 1, the mmWave communication system includes an access point (AP) 111, a plurality of stations (STAs), e.g., N STAs, e.g., an STA#1 113-1, an STA#2 113-2, . . . , an STA#2 113-N.
Referring to FIG. 1, it will be understood that output power of the AP 111, the STA#1 113-1, the STA#2 113-2, . . . , the STA#2 113-N are different. That is, it will be understood that the output power of the AP 111 is greater than the output power of each of the STA#1 113-1, the STA#2 113-2, . . . , the STA#2 113-N.
Link coverage varies according to the difference in the output power, so a mismatch among link coverage, i.e., downlink coverage of the AP 111 and link coverage, i.e., uplink coverage of the STA#1 113-1, the STA#2 113-2, . . . , the STA#2 113-N occurs.
An environment where there is a mismatch between uplink coverage and downlink coverage in a general mmWave communication system has been described with reference to FIG. 1, and a beamforming scheme performed in a general mmWave communication system will be described with reference to FIG. 2.
FIG. 2 schematically illustrates a beamforming scheme performed in a general mmWave communication system according to the related art.
Referring to FIG. 2, it will be assumed that the mmWave communication system is an IEEE 802.11ad communication system.
The mmWave communication system includes an AP 211 and an STA 213.
The AP 211 performs a beamforming operation without considering a location of the STA 213.
The AP 211 repetitively transmits the same packet, e.g., a beacon signal in various directions for Tx beamforming. The AP 211 repetitively transmits the beacon signal during a beacon transmission interval (BTI). In this case, an antenna direction of the STA 213 is quasi-omni-directional.
For Tx beamforming of the STA 213, the STA 213 repetitively transmits the same packet, e.g., a sector sweep (SSW) signal in various directions. The STA 213 repetitively transmits the SSW signal during an association beamforming training (A-BFT) interval. In this case, an antenna direction of the AP 211 is quasi-omni-directional. The AP 211 may transmit, to the STA 213, a sector sweep feedback (SSW-FB) signal to the SSW signal transmitted in the STA 213 within the A-BFT interval. The SSW-FB signal includes information related to an optimal reception (Rx) beam pattern which the AP 211 determines based on the SSW signals transmitted in the STA 213.
As described above, in a beamforming scheme performed in a general mmWave communication system, an AP and an STA perform a beamforming operation independently. So, an interval during which effective data is not transmitted increases, that is, an interval during which a beacon signal and an SSW signal are transmitted increases, and this increases network overhead.
Meanwhile, as illustrated in FIG. 1, in a case that a beamforming operation is performed in a general mmWave communication system, antenna Rx performance may decrease according to a direction of an Rx antenna, link coverage loss may occur due to the decrease in the antenna Rx performance.
In an IEEE 802.11ad communication system in which a scheduling operation is performed on a beacon interval (BI) basis, since the sum of time required for accepting service period request transmitted in an STA and the time which corresponds to a service period allocated by an AP is longer than the time which corresponds to the BI, and therefore, a relatively large network latency occurs.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.